Sleep apnea is a sleep disorder characterized by pauses in breathing during sleep. By definition, sleep apnea is the cessation of airflow to the lungs during sleep which lasts for at least 10 seconds, and is associated with more than a 4% drop of the blood's Oxygen Saturation (“SaO2”) level. There are three distinct forms of sleep apnea: central; obstructive; and complex. Complex sleep apnea is defined as a combination of central and obstructive sleep apnea. It is estimated that central, obstructive, and complex sleep apnea account for approximately 0.4%, 84% and 15% of the reported cases, respectively. With central sleep apnea, a patient's breathing is interrupted by the lack of respiratory effort. With obstructive sleep apnea, a physical block to airflow interrupts patient breathing. With complex sleep apnea, there is a transition by a patient from central sleep apnea characteristics to obstructive sleep apnea characteristics during breathing.
Obstructive Sleep Apnea (“OSA”) is the most common respiratory disorder. OSA may lead to a myriad of problems such as daytime fatigue, poor job performance, and increased risk of accidents. Additionally, OSA may contribute to cardiovascular problems and irritability and patients may not be able to concentrate. OSA is most common in people with high blood pressure, people with a narrowed airway due to tonsils or adenoids, and people who smoke tobacco products. OSA is also known to occur two to three times more often in the elderly, and also more often in males than in females.
Currently, various tests exist to diagnose sleep apnea such as polysomnography (“PSG”). PSG is a preferred diagnostic tool for sleep apnea and includes a comprehensive recording of the biophysiological changes of a patient that occur during sleep. A typical PSG test consists of recording various biological signals including brain signals (“EEG”), heart rhythm signals (“ECG”), muscle activity or skeletal muscle activation signals (“EMG”) of chins and legs, nasal airflow signals, electro-oculogram or eye movement signals (“EOG”), and abdominal and thoracic movement signals. A disadvantage of PSG is the time it takes to gather the biological signals and further the time it takes to evaluate those signals. Another disadvantage of PSG is the expense since the test is administered with a full night of patient supervision by a healthcare professional. Additionally, PSG is neither portable nor convenient for patients. Therefore, many different technological attempts have been made to develop alternative, non-invasive, and portable sleep apnea monitoring tools.
Some of these alternative technologies record a reduced number of signals and detect apnea events during sleep. Many of the current technologies record at least four signals including patient airflow, SaO2, respiratory effort, and snore sound by one or more ambient microphones located within range of the patient. In these technologies, patient airflow may be measured by either a face mask or a nasal cannulae connected to a pressure transducer, and cessation of patient air flow is detected as the main diagnostic sign of sleep apnea, particularly OSA. In the case of mouth breathing by a patient, which may occur often during the night, the nasal cannulae will not register airflow. Therefore, the nasal cannulae is not very reliable. On the other hand, using a face mask, which is considered a more reliable device for airflow measurement, may change the breathing pattern of the patient. Additionally, it is difficult for some patients to fall asleep wearing a face mask.
A majority of people (˜70%) who underwent a full-night sleep study are not diagnosed as severely apneic. Therefore, there is a need for a non-invasive system and methods to pre-screen patients suspected of sleep apnea. The present invention satisfies this demand.